Tektronix TDS3000C Series Manual page 18

Check the Quality of a Communications Signal (continued)
Some communications signals are encoded in a
Quadrature Amplitude Modulation (QAM) format.
To test the distortion of such a signal, engineers
can use the TDS3000C Series to generate a
constellation diagram and analyze the clarity of
the signal's amplitude and phase at discrete
times in the diagram.
To obtain a constellation diagram using the
TDS3000C Series oscilloscope:
1. Connect the three signals to the oscilloscope using
proper probe techniques.
2. Press the front panel Display button.
3. Press the bottom XY Display menu button.
4. Press the side Gated XYZ menu button to select
the Z (gate) source channel.
5. If needed, press the side Ch1 (x) Versus menu button
to select the Y signal (Ch2 is the default).
6. Press the side Gated By menu button to select the
Z (gate) source channel.
7. Rotate the general-purpose knob to enter a value.
8. To properly place and scale the image, adjust the
Vertical Scale and Vertical Position with Ch1
(horizontal) and Ch2 (vertical) selected.
TDS3000C Series Oscilloscopes
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